@Medi Sarwary I can share with you my experiance doing the BRRRR method (Actually I do a slight variation, the BARRRR method (A=Advertise, you do this for tax write of purposes if needed to write off more of the rehab cost right away.

You need to calculate it as investment income - expenses (including annual taxes and income taxes on your gains) - increased equity (loan paydown - that is part of your profit, but it isn't part of your cashflow)If you are looking at this on only a monthly basis, you'll miss annual or semi-annual costs or seasonal variations. 

If you wanted to get really freaky, you could try to come up with an equation dictating the outdoor temperature at which the furnace kicks in based on the ratio of natural gas prices to electricity prices, taking into consideration the variation in efficiency of the heat pump relative to temperatures(but that would be pretty challenging!

(There are some other special variations you can do, but doubt they’re necessary for you) Plenty of good QIs on here that can assist.

my only slight variation is we build new home communities and we are one of the few that will deal with VA loans.. my wife and I believe we owe it to our service men and women to allow them to use those loans even though they are more time consuming for us.. but on the new construction the inspections are no more daunting on older homes it can be a challenge.. 

Firstly, I reckon there is too much variation in the purchase prices.

I know variations of this question have been asked before but can't find this specific question.

Really so many options and variations it can be quite exciting. 

Create your own by adding an accessory dwelling to a single-family house, as detailed in this BP thread from California:https://www.biggerpockets.com/forums/61/topics/732543-here-is-my-adu-variation-to-brrrr-its-called-bra2xrrDC, Arlington, and Montgomery County have all updated their zoning laws in recent years to broadly permit ADUs within or behind owner-occupied houses.

Then just call any investor currently advertising through PPC in my area.I need to talk to 10-20 people who tell me "they'll never move" or "they'll be carried out of here feet first" or some variation......to find the one who says "what's this about?